Mass Spectrometry Spectral Collections

The spectrum is examined first. Before starting any interpretation, it is strongly recommended that a computer or a manual library search is performed to check whether this spectrum belongs to an existing collection. Identification of an unknown compound in this way depends directly on the quality and comprehensiveness of the collection used. However, only libraries of electron ionization spectra are efficient. Other ionization techniques yield spectra that are much too dependent on the instruments and experimental conditions. 

If the spectrum is found, the research is over. However, we must take into account the fact that close isomers often have identical mass spectra, and that sometimes very similar mass spectra belong to different compounds. We cannot blindly trust identification from a comparison. 

Three main spectra collections now exist. The first is the NIST/EPA/NIH mass spectral database, which contains 190 000 spectra of 163 000 compounds [1]. This original collection of spectra and related information is produced by the National Institute of Standards and Technology (NIST) with the assistance of expert advisors from the Environmental Protection Agency (EPA) and National Institutes of Health (NIH). This library is available on CD-ROM for personal computers with integrated tools for GC/MS deconvolution, mass spectra interpretation and chemical substructure identification. This US government publication is very cheap and of very high quality. This library is widely spread in many commercial mass spectrometers. Mass spectra for over 15 000 compounds are accessible on-line [2], 

McLafferty and Stauffer published in The Wiley Registry of Mass Spectral Data a collection of about 380000 spectra of over 200000 compounds [3]. It is the largest and most comprehensive library of reference spectra that contains over 180000 searchable structures and over 2 million chemical names. The eighth edition of The Wiley Registry of Mass Spectral Data is available in electronic format and is compatible with the software of most instrument manufacturers and NIST MSSearch. Furthermore, it is accompanied by an interpretation help program called Probability Based Matching (PBM). 

Mass Spectrometry Principles and Applications, Third Edition Edmond de Hoffmann and Vincent Stroobant Copyright 2007, John Wiley Sons Ltd 

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Markey, S.P., Thobhani, H.A. and Hammond, K.B. (1972), Identification of Endogenous Urinary Metabolites by Gas Chromatography - Mass Spectrometry A Collection of Mass Spectral Data, University of Colorado Medical Center, Denver, Colorado. 

JICST/JOIS. The Japan Information Center for Science and Technology (fICST) Mass Spectral Database is accessible to users in Japan through the JICST Eactual Database System (fOlS-E). The database uses the NIST/EPA/ MSCD data collection supplemented by spectra from the Mass Spectrometry Society of Japan (84). 

Although individual laboratories find it useful to compile their own reference library files, access to very large collections of mass spectra and to published data [55] is essential. A compilation of many thousands of spectra by the Aldermaston Mass Spectrometry Data Centre and the Division of Computer Research and Technology at the National Institutes of Health [56-58] has been made available commercially. The file can be searched in a number of ways using an interactive conversational mass spectral search system via a teletype and acoustic link over telephone lines. 

B. S. Middleditch and J. A. McCloskey, A Guide to Collections of Mass Spectral Data (The American Society for Mass Spectrometry, 1974). 

This paper discusses studies of sea surface films observed and collected in the southern California Bight and the U. S. Middle Atlantic Bight. The goals of these studies were to understand the relationship between chemical composition and surface elasticity in these complex natural films and to determine the range of surface elasticity typical of the ocean surface. Mass spectrometry was the principal analytical tool because of its capacity to characterise and identify chemical structures for many compound classes and to provide a quick assessment of compounds enriched in sea surface films. We present typical variations in SAOM chemical composition as reflected in mass spectral patterns and show the effect of these compositional variations on the film elasticity. 

The mass spectral data selected for multivariate analysis represented a suite of 30 microlayer and bulk surface seawater surfactant samples (fraction FI Frew et al. (2006)) including seven from waters off Monterey and Santa Barbara, California and 23 collected along a transect from Delaware Bay on the U. S. east coast to the Sargasso Sea. Sample extracts were analysed in triplicate by desorption-electron ionisation (DEI) mass spectrometry (Boon 1992 Frew et al. 2006). Individual DEI mass scans were summed over the full desorption/pyrolysis interval, reduced to integer masses, and averaged for processing by multivariate analysis. Elasticities were estimated quasi-statically from surface pressure-area (El A) isotherm measurements in a KSV 2200 Langmuir film balance (Frew et al. 2006). The elasticity data were subsampled at fixed surface pressure intervals (0.5 mN m"1) for comparison with the results of the multivariate analysis. 

Isolation of Metabolites from Poultry Bile for Spectral Identification. Pooled samples of bile from poultry receiving feed medicated at 25 ppm semduramicin sodium for 7 days were extracted with ethyl acetate followed by chloroform. Abundant metabolites were isolated by collection of fractions from repeated injections on a normal phase silica HPLC column. The recovered fractions were analyzed by Fast Atom Bombardment Mass Spectrometry and proton NMR spectroscopy. 

The authors of the papers cited below describe different applications of both ES and APCI mass spectrometry. The LODs reported in these papers differ and are also hard to compare because of different ways of acquiring mass spectral data. Some report LODs as the smallest total amount detected, for example picogramme or femtomol, whereas others express LODs as the concentration injected (pg pl"0- Furthermore, the solvent flow rates differ substantially, from 1 plmin" to lOOOplmin" Finally, both the mass span over which data are collected and the total time of acquiring the data differ considerably. Typically, at a solvent flow rate of 400 pi min" and using gradient LC separation (20 pi loop) with mass spectrometric detection in SIM mode, a LOD of 5-10 fmol pr is achieved. Use of very low solvent flow rates (1 pi min" and the acquisition of data over, say, 3 min may result in lower LODs. This approach is very useful when the amount of sample is limited. 

In our work at Leiden University, apart from HPLC-photodiode array (PDA) detection, HPLC-electrospray mass spectrometry was used as characterization and identification tools. A semipurified taxine extract obtained with acid/base extraction of T. baccata needles was analyzed in reversed phase nine taxines, one taxinine, and six taxanes were found present in the sample. Furthermore, 10-deacetylbaccatin 111 (paclitax-el s main precursor) and other taxanes were also found in the extract. Identification of the peaks was made with online liquid chromatography/mass spectrometry (LC/MS) and off-line nuclear magnetic resonance (NMR) following fraction collection at the end of the HPLC. Retention and spectral data of the identified peaks were used as tool to screen for taxines and taxi-nines in plant and cell culture extracts. Several... 

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